Genotypic variation in response of quaking aspen (Populus tremuloides) to atmospheric CO2 enrichment.

Enriched atmospheric CO2 alters the quantity and quality of plant production, but how such effects vary among plant genotypes is poorly known. We evaluated the independent and interactive effects of CO2 and nutrient availability on growth, allocation and phytochemistry of six aspen (Populus tremuloides Michx.) genotypes. One-year-old trees, propagated from root cuttings, were grown in CO2-controlled glasshouses for 64 days, then harvested. Foliage was analyzed for levels of water, nitrogen, starch, phenolic glycosides and condensed tannins. Of seven plant growth/allocation variables measured, four (biomass production, stem growth, relative growth rate and root:shoot ratio) exhibited marginally to highly significant CO2 × genotype interactions. CO2 enrichment stimulated growth of some genotypes more than others, and this interaction was itself influenced by soil nutrient availability. In addition, enriched CO2 increased the magnitude of the among-genotype variance for four of the growth/allocation variables. Of six foliar chemical constituents analyzed, CO2-mediated responses of two (the phenolic glycoside tremulacin and condensed tannins) varied among genotypes. Moreover, enriched CO2 increased the magnitude of among-genotype variance for four of the chemical variables. Given the importance of these growth and chemical characteristics to the biological fitness of aspen, this research suggests that projected atmospheric CO2 increases are likely to alter the genetic structures and evolutionary trajectories of aspen populations.

Effects of CO2-mediated changes in paper birch and white pine chemistry on gypsy moth performance.

We examined the effects of CO2-mediated changes in the foliar chemistry of paper birch (Betula papyrifera) and white pine (Pinus strobus) on performance of the gypsy moth (Lymantria dispar). Trees were grown under ambient or enriched CO2 conditions, and foliage was subjected to plant chemical assays and insect bioassays. Enriched CO2 atmospheres reduced foliar nitrogen levels and increased condensed tannin levels in birch but not in pine. Foliar carbohydrate concentrations were not markedly altered by CO2 environment. Gypsy moth performance was significantly affected by CO2 level, species, and the CO2 x species interaction. Under elevated CO2 conditions, growth was reduced for larvae fed birch, while development was prolonged for larvae fed pine. Although gypsy moths performed better overall on birch than pine, birch-fed larvae were influenced more by CO2-mediated changes in host quality.